Set the MouseTracker targetElement after binding.
Set the MouseTracker targetElement after binding.

Otherwise the listeners are registered with the wrong value of this.

BUG=
R=nduca@chromium.org

Review URL: https://codereview.appspot.com/12629044

git-svn-id: 3a56fcae908c7e16d23cb53443ea4795ac387cf2@846 0e6d7f2b-9903-5b78-7403-59d27f066143

bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer